The National Football League’s (NFL’s) new policy banning national anthem protests is “flatly illegal,” a Harvard law professor says. And although you may think it’s because of First Amendment considerations, that’s not the entire story.

Writing for Vox, Benjamin Sachs, the Kestnbaum Professor of Labor and Industry at Harvard Law School, lays out the reasons why the NFL’s policy, announced last week to great applause from the Trump administration, is unlikely to stand up to a court challenge.

The First Amendment Only Applies Obliquely Here

You may think that the First Amendment would be the main issue in this case, but it’s not a direct consideration in the national anthem controversy. That’s because, in the main, the guaranteed right to free speech as laid out in the Constitution only means that the government can’t stifle your free speech rights. It says nothing about your employer. Some states, such as California, have extended those protections to the employee/employer relationship, but New York, where the NFL is headquartered, is not one of them.

However, none other than the president of the United States has injected himself into the NFL national anthem controversy. In fact, says Sachs, Trump has “been actively involved in the league’s decision-making process.” And indeed, the NFL instituted the new policy in direct response to the Trump administration’s involvement.

“[The NFL believes] that if they do not ban the protests, the president will continue to make the protests a national issue and thereby negatively affect the league’s income stream.”

That means that a competent lawyer can make a case that the president himself is responsible for the new rule, raising clear and unambiguous First Amendment questions.

“Applying the Constitution in this context is justified but would require judges to break some new legal ground.”

While First Amendment considerations and the indirect involvement of the president make for a juicy court case, the real reason the NFL’s new policy is illegal is much more mundane, says Sachs: it’s a violation of workplace rules.

In short, the NFL instituted the new rule behind closed doors and without input from the players. That violates their union protections.

“When employees, including football players, are represented by a union, the employer — including a football league — can’t change the terms of employment without discussing the change with the union. Doing so is a flagrant violation of the employer’s duty to bargain in good faith.”

What Does All Of This Mean For The NFL?

That’s unclear. While some players, and even some team officials, have complained about the new policy, the NFL does not seem to be interested in talking about changing it. And according to Sachs, it would likely take a lawsuit and a court decision to get the league to change the policy.